Current wireless radio frequency (“RF”) modems that cooperatively operate with a host computing device (“host computer”) typically include: (1) a radio portion, also called an RF front end or an RF head; (2) a modulator/demodulator portion, also called a baseband processing unit or baseband chip; (3) a central processing unit (“CPU”) or processor; (4) memory; and (5) an interface. These modem components collectively operate during a wireless communications process to receive an electromagnetic RF signal in a receive mode, wherein the RF signal contains information to be extracted from the received RF signal, and in a transmit mode, wherein the components work collectively to transmit an electromagnetic RF signal and the RF signal contains the information to be transmitted. Moreover, during the receive and transmit modes, the modem components collectively operate to perform three principal modem functions: RF conversion, baseband processing and protocol stack control.
Typically during RF conversion, the RF head receives the RF signal during the receive mode and converts that RF signal into a modulated baseband analog signal and, during the transmit mode, the RF head converts a modulated baseband analog signal into an RF signal for transmission. During baseband processing, the baseband processing unit in the receive mode demodulates the modulated baseband analog signal by extracting a plurality of data bits that correspond to the information being received. In the transmit mode, the baseband processing unit generates the modulated baseband analog signal for processing by the RF head.
As part of the above wireless communications process, data bits being transmitted are wrapped with protocol bits of data to facilitate transmission, routing, and receiving of the data bits. Likewise, this protocol data must be removed to accurately reproduce, in the receiving RF modem, the data that was sent. The adding or stripping of the protocol bits, also called protocol stack control, is generally performed by the processor in the RF modem under the control of a protocol stack software program stored in the RF modem's memory. Finally, the interface feeds the data bits from the host computer to the RF modem for processing and transmission and feeds to the host computer the reproduced data bits that were extracted from the RF signal.
The host computer may typically be a laptop or palmtop computer, a Personnel Digital Assistant (PDA) such as a PALM Pilot or Handspring, a point of sale terminal, or some other computing system. Typical interfaces between the wireless RF modem and the host computer are RS-232, USB, Parallel Port, IrDa, PCMCIA, or Compact Flash. However, other interfaces are also used, including a variety of proprietary interfaces. Moreover, there are many wireless RF standards that must be considered in the design of any wireless RF modem. Some examples include: circuit switched commercial telecommunications standards including AMPS, CDMA (IS95A & B), and GSM; packet switched standards including CDPD, 1XRTT, GPRS, EDGE, and W-CDMA; and proprietary wide area wireless networks such as Metricom, Re-Flex, FLEX, Mobitex, and ARDIS.
Wireless RF modem use has grown very rapidly during recent years and is projected to continue to grow. Whereas in the past, only a few kinds of host computers were equipped with wireless RF modems, the trend of incorporating such modems is growing, especially with respect to wireless RF modems that plug into laptops and PDAs.
Typically, the detachable wireless RF modems that work cooperatively with host computers perform all of their functions with internal software and hardware. They rely on the host computers only to provide data to be transmitted and a receptacle for data received by the modem from the received RF signal. Accordingly, several hardware components and software functions are typically duplicated in the wireless modem and the host computer. For instance, both the modem and the host computer typically have a CPU, various types of memory, UARTS for serial transmission and reception of data, and other subsystems, with both the modem's and the host computer's CPU operating independently of each other. Such hardware and software duplications result in the high cost of wireless RF modems.
Prior art wireless RF modem architectures are therefore inadequate because they are expensive, consume more power than is needed due to the redundant hardware, take up more space, and weigh more than necessary. What is needed is a wireless RF modem that shares certain components resident in its host computer, thereby enabling the host computer to perform some of the modem's principal functions and thus eliminate the need for redundant hardware in the modem.